1. Field of the Invention
The present invention relates generally to valves for use in high temperature zones, and specifically to valves used in semiconductor equipment for controlling gas flow at high temperatures.
2. Description of the Related Art
High-temperature ovens, called reactors, are used to create structures of very fine dimensions, such as integrated circuits on semiconductor substrates. One or more substrates, such as silicon wafers, are placed on a substrate support inside the reaction chamber. Both the substrate and support are heated to a desired temperature. In a typical substrate treatment step, reactant gases (also referred to as precursors) are passed over the heated substrate, causing the deposition (e.g., chemical vapor deposition, or CVD) of a thin layer on the substrate. CVD is typically conducted at high temperatures, such as 250-900° C.
Deposition equipment normally includes a system for delivering gas to the reaction chamber. The gas delivery system typically comprises a plurality of precursor sources, at least one carrier gas source, a network of pipes for delivering the precursor gases to the reaction chamber, an injection manifold or showerhead for injecting the gas into the chamber, and a number of valves for controlling the gas flow. Also, some precursor sources may be in powder or liquid form, and means for vaporizing such precursors can be provided (e.g., bubblers).
One type of CVD is atomic layer deposition (ALD). In ALD, two complementary precursors are alternatively introduced into the reaction chamber. Typically, a first precursor will adsorb onto the substrate surface, but it cannot completely decompose without the second precursor. The first precursor adsorbs until it saturates the substrate surface; further growth cannot occur until the second precursor is introduced. Thus, the film thickness is controlled by the number of precursor injection cycles rather than the deposition time, as is the case for conventional CVD processes. Accordingly, ALD allows for extremely precise control of film thickness and uniformity. ALD is also conducted at high temperatures, such as 250-900° C.
In ALD, the reaction chamber is typically pulsed with a non-reactive protective gas between injections of the two precursor gases, in an attempt to rid the chamber of any excess of the preceding precursor gas. Otherwise, the excess preceding precursor would intermix and react with the subsequently pulsed precursor to form unwanted CVD-type growth on the substrate surface and/or on surfaces of the chamber.
Also, condensation of the precursors should be avoided in the vicinity of the reaction chamber. Condensation of the precursors, in particular in the conduits between the precursor sources and the reaction chamber as well as on the substrate, will seriously impair the quality of the thin film. The same applies to condensation of solid particles or liquid droplets on the thin film in the reaction chamber. Therefore, an ALD process is operated in such a manner that the temperature in the equipment interconnecting the precursor sources and the outlet of the reaction chamber (the “hot zone”) is not allowed to drop below the highest of the condensation temperatures of the precursors. The temperature of the ALD process is determined by the precursors used and the applied pressure. Generally, the temperature lies in the range between the condensation/evaporation temperature and the decomposition temperature of the precursors.
Polybenzimidazole (PBI) is a high performance polymer with a wholly aromatic molecule of high thermal stability. PBI items are typically made by a powder sintering processes. PBI has excellent high temperature properties (e.g., thermal resistance) and is generally nonflammable, strong, stiff, wear-resistant, plasma-resistant (including oxide etch plasma), and very hard. It has a particularly high strength in and recovery from compression, and a coefficient of thermal expansion of about 23×10−6, which is similar to that of aluminium. Compared to other high performance polymers, PBI displays good chemical resistance to many harsh chemical environments. Despite absorbing (slowly) a high percentage of water at saturation, PBI is stable to hydrolysis and resists high-pressure steam. It also has a low coefficient of friction (e.g., 0.19-0.27). One type of PBI material is Celazole®, which is a trademark of PBI Performance Products, Inc. of Charlotte, N.C., U.S.A. and commercially available from Quadrant Engineering Plastic Products of Reading, Pa., U.S.A.